Grantee Research Project Results

Final Report: Biobeds for Containment and Destruction of Pesticides at Agricultural Mixing and Loading Facilities

EPA Contract Number: 68D00236
Title: Biobeds for Containment and Destruction of Pesticides at Agricultural Mixing and Loading Facilities
Investigators: Lamar, Richard T.
Small Business: EarthFax Development Corporation
EPA Contact:
Phase: I
Project Period: September 1, 2000 through March 1, 2001
Project Amount: $69,683
RFA: Small Business Innovation Research (SBIR) - Phase I (2000) RFA Text |  Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)

Description:

Problem:
Although groundwater contamination by pesticides is largely attributed to non-point sources, pesticide contamination of soil and
groundwater at agrochemical dealerships (Mueller 1989), pesticide mixing/loading sites (Hallberg 1985) and pesticide applicator cleaning sites (Kruger and Seiber 1984) indicates that point sources are also significant sources of groundwater contamination. Indeed, agrochemical storage and handling practices have been targeted as a ?point source? for potential groundwater contamination by federal and state legislation across the United States (Kammel and Walsh 1989). Evaluation of soils and groundwater for pesticide contamination at a variety of pesticide mixing/loading sites indicates that these sites are a point source of contamination and possess the potential for future contamination unless preventative measures are taken. The pesticides found in groundwater at agrochemical handling facilities are, in general, those most frequently used. A summary of data from studies that evaluated frequencies with which different pesticides have been detected in ground water beneath agrochemical handling facilities in Wisconsin and Illinois indicated that the five most frequently detected pesticides-atrazine, alachlor, metolachlor, cyanizine and metribuzin-were also those used most extensively by the facilities included in the study (Barbash and Resek 1996).

The installation of well designed, agrochemical handling facilities referred to as chemical mixing centers (CMCs) or chemical mixing facilities (CMFs) has been proposed by several groups to prevent soil and groundwater contamination associated with improper handling of pesticides (Carter 1994, Wilson 1994, Dwinell 1994). The costs for these engineered facilities have been reported to range from $8,500.00 (Wilson 1994) to $20,000 (Carter 1994) and as high as $40,000 (personal communication with Mr. Michael Broder, National Fertilizer & Environmental Research, Tennessee Valley Authority 1999). The expense of these facilities may be cost prohibitive to the majority of the 1.4 M farms where pesticides are used because of the low net incomes generated by those farms.

Solution:
If pesticide users, the vast majority of who are members of the agriculture community, are to be convinced to adopt practices that prevent pesticide contamination of groundwater at mixing/loading facilities, less expensive alternatives need to be offered. One such alternative that is simple in design, easy and inexpensive to maintain, employs inexpensive materials that are readily available to farmers and that is based on the microbial degradation of pollutants is the concept of biobeds. A biobed is an in-ground treatment unit designed to contain spills of herbicides and other pesticides, even of high doses on limited surfaces, and to destroy the chemicals, through microbiological activity, as rapidly as possible (Torstensson and Castillo 1997). In its simplest form, a biobed is a rectangular excavated hole in the ground (60 cm deep and 0.5 m broader and longer than the sprayer tank or other mixing container) filled with a mixture of top soil and readily available organic amendments such as peat and straw.

Objectives:
The primary objective of the Phase I work was to evaluate the technical feasibility of using biobeds to contain and destroy pesticides at pesticide mixing and loading facilities in the United States. To achieve this objective, the following technical questions were addressed:

1. What is the degradative potential of biobeds towards individual pesticides and pesticide mixtures
   commonly used in the United States?
2. Can substrates, readily available in areas of high pesticide use, be substituted for straw without
   loss of pesticide degradation performance.
3. What is the contribution of leaching to decreases in pesticide concentrations within the biobed?
4. Is there a benefit to biobed performance from inoculation of the biobed mixture with white-rot fungi.
   

Approach:
The technical potential of using biobeds to contain and degrade pesticides was evaluated in a series of experiments using
laboratory-scale biobeds located in greenhouses. In general, experiments involved application(s) of the selected herbicides to the surface of the biobeds that were prepared to assess the various factors (e.g. various substrate mixtures; with and without fungal inoculation) . The herbicide-degrading potential of the biobed substrate mixtures was determined by analyzing soil/peat/(straw or corn stover or corn cob) mixture sub-samples taken from various depths in the beds to determine residual herbicide concentrations over time.

Experiments:
A total of three experiments were conducted to evaluate the herbicide degrading performance of the biobeds. The herbicides
evauated were: atrazine, acetochlor, alachlor and metolachlor. In Experiment #1, the herbicide-degrading performance of a
soil-substrate mixture containing 25% (by volume) top soil, 25% peat moss and 25% straw (Mixture A), which was used by
Torstensson and del Pilar Castillo (1997), was evaluated. In this work barley straw was used in place of wheat straw. In Experiment #2 the effect of replacing barley straw with corn husks or corn stovers on the herbicide-degrading performance of the biobeds was evaluated. The effect of white-rot fungal inoculation on the herbicide-degrading performance of soil-substrate Mixture A was evaluated in Experiment #3. Biobed herbicide-degrading performance was assessed by determining the concentrations of herbicides, initially applied to the surface of the biobeds, at the following depths: 0-5 cm, 5-15 cm, 15-30 cm, 30-45 cm and 45-60 cm.

Summary/Accomplishments (Outputs/Outcomes):

The modification of the original soil-substrate mixture developed by Torstensson and co-workers (Torstennson and Castillo 1997)., with wheat straw substituted with barley straw, had a very high capacity for the degradation of the tested herbicides as evidenced by their half-lives (T_1/2) under the various tested biobed conditions (Table 1).. The half-lives of the herbicides obtained in this study were either much lower, in the case of atrazine, or well within the ranges of literature reported half-lives for the same herbicides (Table 2). The initial herbicide concentrations in the 0 to 5 cm surface layer that were evaluated in this work were, in some cases, three orders of magnitude greater than pesticide residue concentrations reported by Torstennson and Castillo (1997) during the spraying season. Despite these high initial concentrations (e.g. > 1000 mg kg-1) the degradation of all the tested herbicides was rapid and extensive.

Table 1. Half-lives (T_1/2)¹ of the tested herbicides in the upper 0 to 5 cm layer in biobeds.

	Atrazine		Acetochlor			Alachlor		Metolachlor
Soil-Substrate				(T1/2-days)
Mixture
Experiment #1
Mixture A2	2.2		5.5			27.3		29.6
Experiment #2
Overall3		4.8			14.9
Mixture A			7.3			17.5
Mixture B			8.6			9.8
Mixture C			2.7			16.9
Experiment #3
Overall4	0.62							27.8
Non-inoculated	0.14							27.3
Phanerochaete sordida	1.89							27.1
Pleurotus ostreatus	1.02							26.8

¹Half-lives were determined using least squres plots of log (Y) = a + b(x)^0.5, where Y equals the concentration of herbicide in mg kg^-1 and X equals time in days.
²All mixtures were composed of 25% top soil and 25% peat moss (by volume). The bulk was made up of: Mixture A 50% barley straw; Mixture B 50% corn stovers; Mixture C 50% corn cobs
³Overall = overall soil-substrate mixture treatments.
⁴Overall = overall fungal treatments (i.e. including the non-inoculated treatment).

The chloroacetanilide herbicides (e.g. alachlor, acetochlor and metolachlor) are generally known to degrade more quickly in the soil than triazine herbicides, including atrazine (Scribner et al. 2000)., with typical half-lives for the chloroacetanilides ranging from 15 to 30 days (Leonard, 1988)., compared to 30 to 60 days for triazines (Ferrer et al., 1997). This is contrary to the rates of disappearance observed in this work for the herbicides in the biobeds with atrazine degradation equaling or exceeding the rate and extent of degradation of the most labile chloroacetanilide, acetochlor (Table 1).. Therefore, the microbial communities that were produced in the biobeds appeared to be particularly suitable for atrazine degradation.

Table 2. Reported half-lives for atrazine, acetochlor, alachlor and metolachlor.

Atrazine	Acetochlor	Alachlor	Metolachlor	Reference
15-54			36-71	Topp et al., 1994
50-265				Obrador et al., 1993
37				Jenks et al. 1998
31-54		15-77		Workman et al., 1995
	5-8	4-8	9-19	Mueller et al., 1999
		9-11	17-23	Zimdahl and Clark, 1982
			11-14	Braverman et al., 1986
		11-24	39-70	Walker and Brown, 1985
		8		Beestman and Deming, 1974
		20-39		Jurado-Exposito and Walker,1998
		14-31		Guo and Wagenet, 1999
			18	Sanyal and Kulshrestha, 1999
		24		Weed et al., 1995
		18-45		Walker et al., 1992
		6		Wienhold and Gish, 1994
		20-40		Walker and Welch, 1991
		7-20		Jones et al., 1990

As had been observed in previous soil studies (Jenks et al., 1998), the rate of atrazine degradation decreased with increasing
soil-substrate mixture depth. However, even at the lower soil-substrate mixture depths (i.e. 30 to 45 cm and 45 to 60 cm), atrazine degradation was extensive. The half-lives for atrazine that were observed in Experiments #?s 1 and 3 (Table 1) are extremely short compared to those reported in the literature (Table 1). Initial atrazine concentrations in the biobed experiments were in the range of 1000 mg kg-1 in Experiment #1 and as high as approximately 7000 mg kg-1 in Experiment #3. This is much higher than surface soil concentrations that result from atrazine field applications that are in the single digit mg kg-1 (Workman et al., 1995). Atrazine concentration over the range of 5 to 5000 mg kg-1 did not affect the rate of degradation (Gan et al., 1996). Thus, the greater rates of degradation were probably due to the active microbial population produced in the biobeds rather than increased degradation as a result of higher initial atrazine concentrations.

Persistence of chloroacetanilide herbicides in the field soils widely depending on soil type, temperature, soil water, and depth below the soil surface (Kotoula-Syka et al., 1997). Metolachlor is the most persistent acetanilide (Walker and Brown, 1985; Zimdahl and Clark, 1982) and had a average half-live (13.7 days) in three soils that was approximately two times as long those observed for alachlor and acetochlor (Mueller et al., 1999). This is similar to what we observed in the biobeds. The average half-life of metolachlor (27.7 days) was 1.7 times and 4.8 times longer than the average biobed half-lives of alachlor and acetochlor, respectively. Alachlor degradation in soil was enhanced by the addition of manure (T1/2 = 21.8 days) and alfalfa (T1/2 = 14.4 days) compared to unamended soil (T1/2 = 24.9 days) (Guo and Wagenet, 1999). The authors speculated that although both manure and alfalfa would enhance alachlor adsorption, the increased supply of nutrients associated with the substrates, compared to unamended soil, probably stimulated microbial growth and, therefore, the rate and extent of alachlor degradation. Alachlor was degraded more rapidly in biobed soil-substrate mixtures containing corn stovers (T1/2 = 9.8) compared to soil-substrate mixtures containing barley straw (T1/2 = 17.5 days) or corn cobs (T1/2 = 16.0 days) (Table 8). Corn stovers have a higher protein, and thus greater nitrogen content than either barley straw or corn cobs. Thus, the enhanced nutrient status in the soil-substrate mixtures containing corn stovers may have been indirectly responsible for the decrease in alachlor persistence compared to soil-substrate mixtures containing either barley straw of corn cobs. However, acetochlor degradation was most rapid in soil substrate mixtures containing corn cobs, not corn stovers.

Degradation of all of the tested herbicides was rapid and extensive. Although there was some evidence of herbicide leaching from upper to lower depths in the soil-substrate mixtures, there was no accumulation of any of the herbicides at any depth. As expected, degradation of the barley straw, corn stovers and corn cobs occurred to varying degrees. Degradation of the barely straw and corn stovers was the greatest and resulted in about a 15 to 25 cm decrease in total biobed depth. Corn cobs, did not degrade as much, resulting in much less of a decrease in total biobed depth. The ability of a substrate to support herbicide degradation and maintain biobed depth over time is an important consideration in biobed maintenance (i.e. frequency of substrate replacement). Biobeds appear to be a technically sound alternative for containment and degradation of pesticides at mixing and loading facilities.

References:

1. Barbash, J. E. and E. A. Resek. 1996. Chapter 8 pp. 323-334. In: Pesticides in Groundwater-
Distribution, Trends and Governing Factors. Chelsea, MI Ann Arbor Press.
2. Beestman, G. B. and J. M. Deming. 1974. Agron. J. 66:308-311.
3. Braverman, M. P., T. L. Lavy, and C. J. Barnes. Weed. Sci. 34:479-484.
4. Carter, R. V., Jr. 1994.. pp. 199-202. In: (Campbell, K. L., W. D. Graham, and A.B. Bottcher, eds.)
Environmentally Sound Agriculture Proceedings of the Second Conference, Orlando, FL. ASAE.
5. Dwinell, S. E. 1994. pp. 152-155. In: Conference Proceedings Pesticide and Fertilizer
Containment Symposium. Midwest Plan Service MWPS-C2.
6. Gan, J., R. L. Becker, W. C. Koskinen, and D. D. Buhler. 1996. J. Environ. Qual. 25:1064-1072.
7. Guo, L. and R. J. Wagenet. 1999. Soil Sci. Soc. Am. J. 63:443-449.
8. Hallberg, G. 1985. North Centeral Weed Control Conf. Proceedings 40:130-147.
9. Jenks, B. M., F. W. Roeth, A. R. Martin, and D. L. McCallister. 1998. Weed Sci. 46:132-138.
10. Jones, Jr., R. E., P. A. Banks, and D. E. Radcliffe. 1990. Weed Sci. 38:589-597.
11. Juardo-Exposito, M. and A. Walker. 1998. Weed Research 38:309-318.
12. Kotoula-Syka, E., K. K. Hatzios, D. F. Berry, and H. P. Wilson. 1997. Weed Technol. 11:403-409.
13. Mueller, W. 1989. Dealers at the source. Agrichem. Age 33:10-12.
14. Mueller, T. C., D. R. Shaw, and W> W> Witt. 1999. Weed Technology 13:341-346.
15. Krueger, R. F. and J. S. Seiber. 1984. Symposium Series 259, American chemical society,
Washington, D.C. pp. 368.
16. Obrador, A., Y. Lechon, and L. Tadeo. 1993. Pestic. Scie. 37:301-308.
17. Sanyal, D. and G. Kulshrestha. 1999. Biol. Fertil. Soils 30:124-131.
18. Scribner, E. A., E. M. Thurman, and L. R. Zimmerman. 2000. Sci. Total Environ. 248:157-167.
19. Topp, E., W. N. Smith, W. D. Reynolds, and S. U. Khan. 1994. J. Environ. Qual. 23:693-700.
20. Torstensson, L. and M. d. P. Castillo. 1997. Pest. Outlook June:24-27.
21. Walker, A. and S. J. Welch. 1991. Weed. Res. 31:49-57.
22. Walker, A. and P. A. Brown. 1985. Bull. Environ. Contam. Toxicol. 34:143-149.
23. Walker, A., Y. H. Moon, and S. J. Welch. 1992. Pestic. Sci. 35:109-116.
24. Weed, D. A. J., R. S. Kanwar, D. E. Stoltenberg, and R. L. Pfeiffer. 1995. J. Environ. Qual. 24:68-79.
25. Weinhold, B. J. and T. J. Gish. 1994. J. Environ. Qual. 23:292-298.
26. Wilson, J. T.pp. 1994. pp. 184-190. In:Enviornmentallyt sound Agriculture. Proceddings of the 2nd Conf. Amer. Sioc.
Agric. Eng. 04-94.
27. Workman, S. R., A. D. Ward, N. R. Fausey and S. E. Nokes. 1995. Trans. ASAE 38:1421-1425.
28. Zimdahl, R. M. and S. K. Clark. 1982. Weed Sci. 30:545-548.

Conclusions:

1. The degradative performance of biobeds toward several of the most commonly used herbicides in the
   U.S. was exceptional,. particularly for the most heavily used herbicide in the U. S., atrazine. Indeed,
   the ability of biobeds to degrade herbicides, as demonstrated by Torstensson and co-workers and in
   the work reported here, suggests that they might also be useful for remediation of pesticide-
   contaminated soils.
   
   
2. Substitution of barley straw with either corn stovers or corn cobs had no effect or enhanced the
   herbicide-degrading performance of biobeds. Therefore, all three of these readily available and
   inexpensive agricultural residues can be used as substrates in biobeds.
   
   
3. Herbicide leaching within the biobeds was not a factor. Herbicide that leached from upper to lower
   levels was degraded over time with the result that there was no accumulation of herbicide at lower
   levels in the biobeds.
   
   
4. Inoculation of biobeds with two species of WRF did not significantly enhance degradation of the
   herbicides evaluated in this work. However, with the wide variety of pesticides used, future use of
   WRF to enhance herbicide degradation in biobeds should not be ruled out.

Supplemental Keywords:

Pesticide containment, pesticide soil remediation, biostimulation., Sustainable Industry/Business, RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Waste, Toxics, Ecological Indicators, Chemical Engineering, Engineering, pesticides, Ecosystem Protection, chemical mixtures, Chemistry, Agricultural Engineering, Agronomy, Environmental Chemistry, Ecosystem/Assessment/Indicators, Analytical Chemistry, Chemistry and Materials Science, Ecological Effects - Environmental Exposure & Risk, cleaner production/pollution prevention, Ecological Effects - Human Health, Chemical Mixtures - Environmental Exposure & Risk, Environmental Engineering, agrochemcial, agricultural mixing/loading , agricultural environments, pollution prevention, pesticide exposure, agriculture, biobeds